The present disclosure relates to a pixel circuit included in a pixel of a display panel. The present disclosure also relates to a display panel in which a plurality of pixels each including the above-described pixel circuit are two-dimensionally disposed and a display device which has the display panel. Further, the present disclosure relates to an electronic unit including the above-described display device.
In recent years, in the field of display devices for displaying images, display devices are developed and commercialized which use, as a light-emitting element of a pixel, an optical element of a current driven type, such as an organic EL (electro luminescence) element, whose light-emission luminance is varied according to a current value flowing therein. Unlike a liquid crystal element and the like, the organic EL element is a self-luminous element. Therefore, since a light source (backlight) is not necessary, a display device (organic EL display device) using the organic EL element provides higher image visibility, decreased power consumption, and higher response speed of element in comparison with a liquid crystal display device which necessitates a light source.
Similarly to liquid crystal display devices, the driving method for organic EL display devices includes a simple (passive) matrix method and an active matrix method. The former has a risk that it is difficult to realize a large-size and high-definition display device, although the structure thereof is simple. Therefore, currently, the active matrix method is actively developed. In this method, a current flowing through a light-emitting element in each pixel is controlled by an active element (in general, TFT (Thin Film Transistor)) provided in a drive circuit provided for each light-emitting element. The pixel circuit includes a plurality of active elements (in general, TFT (Thin Film Transistor)), a capacitative element and the like (see, Japanese Unexamined Patent Application Publication No 2009-300697).
FIG. 16 illustrates a schematic configuration of each pixel of the display device described in Japanese Unexamined Patent Application Publication No 2009-300697. The pixel described in FIG. 16 is made up of an organic EL element D100 and a pixel circuit 100 connected to the organic EL element D100. The pixel circuit 100 has a circuit configuration of 2Tr1C and is made up of a transistor T100 used for a sampling, a holding capacitor C100, and a transistor T200 used for a drive. A write line WSL is formed to extend in a row direction, and connected to a gate of the transistor T100. A power source line PSL is also formed to extend in a row direction, and connected to a drain of the transistor T200. The signal line DTL is formed to extend in a column direction, and connected to a drain of the transistor T100. A source of the transistor T100 is connected to a gate of the transistor T200 used for a drive and one end of the holding capacitor C100. A source of the transistor T200 and the other end of the holding capacitor C100 are connected to an anode of the organic EL element D100. A cathode of the organic EL element D100 is connected to a ground line GND.
Next, operations (operations from turning off to turning on of light) of a pixel described in FIG. 17 are explained. (A) to (C) of FIG. 17 illustrate exemplary waveforms of voltages applied to the pixel described in FIG. 16. Specifically, (A) to (C) of FIG. 17 show a state where two kinds of voltages (Vss and Vcc) are applied to the power source line PSL, a state where two kinds of voltages (Vsig and Vofs) are applied to the signal line DTL, and a state where two kinds of voltages (Von and Voff) are applied to the write line WSL, respectively. (D) to (F) of FIG. 17 show temporal changes of a gate voltage Vg and a source voltage Vs of the transistor T200 in response to voltages applied to the power source line PSL, the signal line DTL, and the write line WSL.